1. Field of the Invention
The present invention relates to a magnetic layered material, a magnetic storage/read system and a magnetoresistive device, and particularly to a magnetic storage/read system having a high recording density.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2-61572 discloses layered films in which electric resistance varies in accordance with an angle formed by magnetization directions of ferromagnetic layers separated by an intermediate layer, a magnetic field sensor and a magnetic storage system, as well as an iron-manganese alloy thin film.
Japanese Unexamined Patent Publication No. 6-60336 discloses means for achieving a vertical magnetization direction of a magnetic layer, or particularly, a magnetoresistive sensing system having a hard magnetic film, and describes a magnetoresistance sensor of which the magnetic layer comprises Co or a Co-based alloy.
Japanese Unexamined Patent Publication No. 6-762247 discloses a magnetic storage system using a nickel-manganese alloy thin film.
Exchange coupling of a chromium-manganese alloy film and a nickel-iron film is reported in the digest of the 19th Annual Conference on Magnetics Japan (1995), pp. 352.
Japanese Unexamined Patent Publication No. 5-266436 discloses a magnetoresistive sensor in which a thin film material arranged in an interface between a non-magnetic layer and ferromagnetic layer is separated by the non-magnetic layer.
Japanese Unexamined Patent Publication No. 6-11252 discloses a magnetoresistive sensor in which a soft magnetic intermediate layer is adhered between a ferromagnetic layer and an antiferromagnetic layer.
In the conventional art, it is difficult to achieve a magnetic storage system having a sufficiently high recording density, particularly a magnetoresistive device acting on an external magnetic field with a sufficiently high sensitivity and output in a reproduction part thereof, and it is further difficult to obtain satisfactory characteristics with a sufficiently inhibited noise, or to achieve functions as a storage system.
In order to improve the recording density, it is necessary to make narrower a unit of recording area on a recording medium, and this in turn requires downsizing of the reproducing part of a magnetic storage system. In this case, two problems are posed: first, for a small device, the shape anisotropy of a device and portion or the like cannot be disregarded, which may easily lead to a decrease in output; and secondly, a magnetic wall has an important effect, which may easily cause noise.
It is known at present that a multilayer formed by laminating ferromagnetic layers via a non-magnetic layer has a large magnetoresistance known as giant magnetoresistance. In such a multilayer the magnetoresistance brings about change of electric resistance in accordance with the variation of an angle made between the magnetizations of two ferromagnetic layers separated by the non-magnetic layer. When using this giant magnetoresistance in the form of a magnetoresistive device, a structure called a spin-valve is proposed. More particularly, this structure comprises an antiferromagnetic layer/a ferromagnetic layer/a non-magnetic layer/a ferromagnetic layer substantially pinning (fixing) magnetization of the ferromagnetic layer in intimate contact with the antiferromagnetic layer by the action of an exchange coupling field produced on the interface thereof, and causing the magnetization of another ferromagnetic layer to be rotated under the effect of an external magnetic field. The effect of the foregoing pinning is herein referred to as pinning bias, and the layer producing this effect, as a pinning bias layer. For the purpose of obtaining a linear output to the external magnetic field, the direction of the pinning bias, i.e., the direction of the exchange coupling field of the antiferromagnetic layer is preferably in the direction of the field to be sensed. In the case of a magnetic head, this is generally in parallel with the MR height direction.
For restraining noise caused by domain wall migration of a magnetoresistive device, on the other hand, an effective way is to made a magnetoresistive layer become a single domain, and it is effective to apply a longitudinal bias to the magnetoresistive layer in a direction making a right angle to the direction of the magnetic field to be sensed. That is, in addition to the disappearance of the magnetic wall, it is thus possible to set the direction of magnetization so that the magnetization process is generated by rotation. As means to apply the longitudinal bias, a method is known which comprises arranging a hard magnetic layer or a ferromagnetic layer to which an exchange coupling field is applied by an antiferromagnetic layer, in contact with an end of the magnetoresistive film in the track width direction, and using a static magnetic field leaking as a result of remanent magnetization. For a magnetic head, the direction of remanent magnetization or exchange coupling field is identical with the track width direction.
As described above, a magnetic head capable of coping with a high recording density is preferably configured, by use of a giant magnetoresistance, so that the longitudinal bias for achieving a single domain is applied while using a spin-valve type magnetoresistive layer film. An antiferromagnetic layer is needed for any one or both of pinned bias and longitudinal bias of the layered film.
Publicly known antiferromagnetic layers are an iron-manganese alloy layer and a nickel-manganese alloy layer, which, however, involve problems in material. The following five features are required for an antiferromagnetic layer material used in a magnetic storage/read system: (1) a large exchange coupling field; (2) properties are maintained even against temperature increase of over 100.degree. C.; (3) properties can occur with a thin layer having a thickness of under 50 nm; (4) the magnetizing process does not require a complicated step such as, for example, a heat treatment for a long period of time; and (5) a sufficient resistance against environment to which the film is exposed. The foregoing known materials, when checked up with the above-mentioned requirements, still have problems in material as to temperature properties, corrosion resistance and simplification of process. These conventional materials have made it very difficult to achieve a magnetic storage/read system of a high recording density, and particularly, a reliability as a system.
As shown in the publicly known examples, however, an antiferromagnetic material excellent in corrosion resistance and temperature properties was found among Cr--Mn-based alloy thin films. A remaining problem is to obtain a large exchange coupling as described in (1) above. The reason is that, according to the known example, the exchange coupling field by a Cr--Mn-based alloy is about 20 Oe per 40 nm NiFe thin film at room temperature. If it is possible to increase this to about twice as high, it will make a large improvement of reliability of such an apparatus using this as, for example, a magnetic head of a magnetic storage/read system.
There is also a problem of thermal stability of a magnetoresistive film. Since the component elements of the foregoing spin-valve film are from about several nanometers to 10 nanometers in thickness, thermal stability is generally low. Improvement of thermal stability is effective for keeping high performance as a sensor or a medium and further for improving reliability.